The desirability of monitoring the use and remaining quantities of consumable printing materials in electrophotographic printing devices has been recognized almost since the inception of the technology itself. As such devices came into use in virtually every place of business in one form or another, the need for a practical and reliable way to sense, for example, toner level in a laser printer or copier, became increasingly apparent. To this end, various systems and methods have been proposed for directly or indirectly sensing the level of consumable flowable materials in printing devices.
One such system is described in U.S. Pat. No. 4,989,754 to Grasso et al., which is directed to a toner cartridge having a low toner sensing mechanism. The mechanism includes a rotatable arm assembly internal to the cartridge, upon which is mounted a magnet. A reed switch is located outside the cartridge. Leads attached to the reed switch are designed to close a circuit when the magnet, due to insufficient levels of toner inside the cartridge, comes into proximity with the switch. Closure of the circuit produces warning indications to the operator of the printer.
Another device is set forth in U.S. Pat. No. 5,049,989 to Arthur et al. This patent describes an ink jet printhead including a carriage having a housing upon which a memory element is mounted. The memory element may be a strip of magnetic media, a semiconductor memory, or an optical medium. A read/write head is mounted in proximity with the path of travel of the printhead, and reads and/or updates information on the memory element each time the printhead passes its location.
U.S. Pat. No. 5,634,169 to Barry et al. discusses a cartridge for a printing device in which a multiple function encoder wheel is used to generate characteristic information about the cartridge. The wheel employs a paddle traveling through the toner material, and acts in conjunction with a coded wheel reader to indicate a component of resistance, thus giving an indication of the amount of toner remaining in the cartridge.
Yet another system is disclosed in U.S. Pat. No. 5,708,912 to Lee, in which a non-volatile memory is used to store data values representing various characteristics of a printing device. The system employs a piezoelectric toner sensor mounted within the cartridge.
It can be seen from these exemplary patents that the problem of directly sensing print media levels, particularly levels of materials such as toner and ink, has been the subject of a great deal of inventive effort. Unfortunately, despite these efforts, several problems remain. For example, mechanical sensors using magnets, piezo elements, and the like are relatively expensive and often unreliable. Furthermore, they frequently extend through the wall of the toner reservoir, increasing the difficulty of manufacturing the cartridge and introducing the possibility of leaks. Methods such as encoder wheels and embedded nonvolatile memory chips avoid such problems by approximating the amount of toner used through tracking print quantities. However, these systems usually require complicated and expensive multi-lead interconnects, which are frequently more expensive than the memory chips themselves.
Even the relatively simple solution proposed in the patent to Arthur et al. has its drawbacks. The system necessitates movement of the printing head past the read/write head in order to function. Thus, the print head is required to execute otherwise unnecessary movement in order to register information on ink levels and other system parameters.
It is apparent from the foregoing that the need exists for a cartridge assembly having a consumable material level monitoring system that will minimize the complexity and expense involved in manufacturing the cartridge while providing a reliable source of system status information.